(1) Field of the Invention
The present invention relates to a semiconductor integrated circuit (IC) device, more particularly to a semiconductor IC device such as an IC chip of a memory device or an input/output (I/O) control device which is selected and used by an address signal from a central processing unit (CPU).
(2) Description of the Prior Art
Generally, in a computer system, a plurality of peripheral circuits such as memory devices and I/O control devices are used. Each of the peripheral circuits may, for example, be a peripheral large scale integration (LSI) chip and include a memory device or an I/O controls circuit which control various I/O devices.
In such a computer system, when the CPU accesses a peripheral IC chip, it is necessary to input a chip select signal to the chip select terminal of the peripheral IC chip and, thereafter, to input data to or output data from the peripheral IC chip.
A computer system using conventional peripheral IC devices requires an address decoder. Thus, the interface circuit between the CPU and each LSI is complex. Moreover, the address of each peripheral LSI is absolutely determined in correspondence to the structure of the address decoder. Thus, it is impossible to use a program designed for one computer system in another computer system using the same CPU, if the addresses of the peripheral LSI's do not coincide with that of the former computer system. Therefore, software for computer systems using conventional peripheral IC's is generally not interchangeable.